The invention is based on a method for monitoring a cooling fluid circuit in an internal combustion engine.
In modern reciprocating piston internal combustion engines for motor vehicles, the heat transmitted to a cylinder head and cylinder block through a wall of a combustion chamber is essentially dissipated by means of a cooling fluid. The cooling fluid is circulated by means of a pump, which is as a rule mechanically driven by the internal combustion engine. There are also known embodiments in which a controllable electric motor is used as a pump drive unit. A regulating valve conveys the cooling fluid through a radiator or through a bypass line, which is provided parallel to the radiator. In addition to the radiator, a heating system heat exchanger for the passenger compartment is also connected to the cooling fluid circuit. A desired temperature of the cooling fluid, possibly controlled by means of a characteristic field, is set so that the permissible temperatures of the cooling fluid and of the components to be cooled are never exceeded during operation.
DE 41 09 498 A1 has disclosed a device and a method for a very sensitive regulation of the temperature of an internal combustion engine. To this end, a control device is supplied with a number of input signals, e.g. the temperature of the engine, the speed and load of the engine, the vehicle speed, the operating state of an air conditioning or heating system of the motor vehicle, and the temperature of the cooling water. A desired value transmitter of the control unit takes the input signals into account when establishing a desired value for the temperature of the engine. According to a comparison of the actual values to the desired values, the control unit controls a three-way valve, which is disposed in the mouth region of a bypass line in a line between the engine and a radiator. Depending on the position of the three-way valve, the inlet flow is distributed to the radiator inlet and to the bypass line. Therefore a cooling of the engine is detected not only as a function of operating parameters that are of direct significance to the temperature build-up, but also as a function of parameters of additional units, which only influence the temperature indirectly. Furthermore, the possibilities for setting the optimal temperature are broadened significantly since malfunctions can also be detected and taken into account. The association of different operating conditions with different ranges of desired temperature values permits the desired temperature to be quickly adjusted, which can be further refined through different priorities of the operating conditions.
For the emissions behavior of an internal combustion engine, it is of crucial importance that the engine reach its optimal operating temperature as rapidly as possible and maintain this temperature for the duration of its operation. This essentially depends on the temperatures of the heat-conducting components that constitute the combustion chamber, in particular the walls of the cylinders, the cylinder block, and the cylinder head. The temperatures in turn depend on operating parameters such as the speed and load of the engine, the volumetric flow and temperature of the cooling fluid, and the load changes, etc. The interrelationships among these parameters and the temperature of the components are extremely complex and cannot be calculated analytically. In order to assure a uniformly good emissions behavior of the internal combustion engine over its entire service life, it is therefore necessary to monitor the proper function of the cooling fluid circuit.